Growth of monolayer graphene on nanoscale copper-nickel alloy thin films

Abstract

Growth of high quality and monolayer graphene on copper thin films on silicon wafers is a promising approach to massive and direct graphene device fabrication in spite of the presence of potential dewetting issues in the copper film during graphene growth. Current work demonstrates roles of a nickel adhesion coupled with the copper film resulting in mitigation of dewetting problem as well as uniform monolayer graphene growth over 97 % coverage on films. The feasibility of monolayer graphene growth on Cu-Ni alloy films as thin as 150 nm in total is also demonstrated. During the graphene growth on Cu-Ni films, the nickel adhesion layer uniformly diffuses into the copper thin film resulting in a Cu-Ni alloy, helping to promote graphene nucleation and large area surface coverage. Furthermore, it was found that the use of extremely thin metal catalyst films also constraint the total amount of carbon that can be absorbed into the film during growth, which helps to eliminate adlayer formation and promote monolayer growth regardless of alloying content, thus improving the monolayer fraction of graphene coverage on the thinner films. These results suggest a path forward for the large scale integration of high quality, monolayer graphene into nanoelectronic and nanomechanical devices.

Controlling the number of layers in graphene using the growth pressure

“…In CVD graphene grown on copper, the copper surface that serves as the catalyst for graphene synthesis becomes covered with the graphene which prevents the copper from catalyzing more graphene growth and thus inhibiting multilayer graphene growth [15]. One approach to overcome this challenge has been to grow graphene on Cu-Ni alloys [16,17]. The presence of Ni in the Cu-Ni alloy helps to increase the carbon solubility in the alloy and thus promotes multilayer growth.…”

“…However, the increased carbon solubility makes growing uniform graphene on these Cu-Ni alloys difficult, which generally results in large variances in the number of layers across the sample grown using this method [17,18].…”

Towards Repeatable, Scalable Graphene Integrated Micro-Nano Electromechanical Systems (MEMS/NEMS)

“…However, the thermal stability of thin-films is reduced as the thickness is reduced. Graphene grown on thin films below 100 nm of Cu and Pt thin film thicknesses show that dewetting can occur at a temperature lower than its melting point [193,198,199]. Thermal instability of thin-films can be verified by Young's Equation (2) where R is the average grain size, t is the thickness of film, and θ is the wetting angle of the metal to the substrate [200].…”

“…Cu thin film has been a good foundation of graphene growth on thin films and has shown device performance comparable to exfoliated graphene as long as crystalline structure of Cu thin film can be maintained in (111) [202]. However, the adhesion of thin film Cu is not sufficient on Si/SiO 2 substrates which causes the thin film to dewet and deform even below the melting temperature of Cu [198]. Therefore, adhesion layers such as Ni, Ti, Ta, and Cr are required between the substrate and Cu layer.…”

Transparent Conductive Electrodes Based on Graphene-Related Materials

“…Unlike Ni, Cu has a low carbon solubility, which makes it possible to grow monolayer graphene with a grain size of several centimeters on Cu foil using a mixture of methane and hydrogen gas at a high temperature of 1000°C as shown in Figure 1a–c and Figure 2; the sheet resistance was reported to be 125 Ω·sq −1 at 97.4% transparency [12]. It has also been demonstrated that Cu–Ni alloy can be used to produce monolayer and multilayer graphene using CVD with methane gas as precursor, since the carbon solubility can be controlled by adjusting the atomic fraction of Ni in Cu (Figure 1d) [39,75,76,77,78,79]. For example, Chen et al presented the CVD synthesis of large-area, primarily bilayer, graphene on Cu–Ni foil by the use of a cold-wall reactor with methane and hydrogen as precursors [74].…”